The rhesus monkeys will be given diets containing 2.0 and 25.0 parts per trillion (ppt) TCDD (2,3,7,8-tetrachlorodibenzo-rho-dioxin) for one year. During this time they will be evaluated clinically. After 6 months on the diet they will be bred. Conception rate, abortions, fetal and neonatal development will be observed. Tissue levels of TCDD will be monitored through periodic fat biopsies. Levels of TCDD in mother's milk will be determined throughout lactation. Attempts will be made to rebreed the rhesus females that are receiving 50 ppt TCDD. If successful, the females as well as their offspring will be evaluated for abnormalities. Following four months of nursing, the infants will be weaned and subsequently evaluated psychologically. If it is impossible to breed the animals on 50 ppt TCDD, they will be removed from the experimental diets and permitted at 6 month recovery period prior to additional attempts at rebreeding. In addition the three surviving animals from the 500 ppt TCDD experiment will continue to be evaluated for recovery from TCDD intoxication and possible development of additional changes that may arise from dioxin exposure. In addition, the animals on the hexachlorodibenzo-rho-dioxin will continue receiving HCDD at 5 parts per billion (ppb) in the diet in order to compare the toxicological effects of the two dioxins.